1. Field of the Invention
The present invention relates to a reverse osmosis membrane including an ultra-hydrophilic passivation layer and a method of manufacturing the same, and more particularly, to a reverse osmosis membrane having an improved performance thereof by forming an ultra-hydrophilic passivation layer on the reverse osmosis membrane, and a method of manufacturing the same.
2. Description of the Related Art
A reverse osmosis membrane may be applied in various industrial fields, for example, in desalting of brine, in preparing ultra-pure water, in treating environmental contamination, etc., and may be found in every daily life. As a membrane of the next generation, a membrane having a high quality including a polymer material having a particular function has been required. The function and properties of the material are necessary to be controlled minutely according to the application purpose of the membrane.
In order to improve the reverse osmosis membrane, a post-treating method using various chemical materials, a method of using an additive during forming a membrane may be used. According to the post-treating method, a plurality of reverse osmosis membranes is coated with polyvinyl alcohol (PVA) or a vinyl acetate homopolymer having a self-crosslinking functionality. Concerning the method of using the additive, a polymer additive may be used while forming various membranes, particularly, a nano filtering membrane to mix the polymer additive with the membrane.
As important improvements obtainable through modifying the exterior surface of the membrane, the stabilization of a separation member for conducting the separation of fouling while operating for a long time, and the increase of the degree of salt rejection for balancing the loss of the flowing amount due to the change of the membrane transferring characteristic, may be illustrated.
Generally, the upper layer of a reverse osmosis membrane is a ultra-thin barrier layer or a separation layer and includes cross-linked polyamide or polysulfone amide having a thickness of 10 to 100 nm. Generally, polyamide may be prepared by an interfacial polymerization method using m-phenylenediamine (MPD) in an aqueous phase and trimesoyl trichloride (TMC) in an organic phase.
The second layer or a middle layer commonly includes an engineering plastic such as polysulfone and commonly has a thickness of about 40 μm. The second layer provides the uppermost layer with a hard and smooth surface. The upper layer may be treated under such a high operation pressure, for example, 10 to 2,000 psi, due to the second layer.
The third layer or a base layer is commonly a non-woven polyester, for example, polyethylene terephthalate (PET) web and commonly has a thickness of about 120 μm. The third layer or the base layer is commonly very porous and irregular. Thus, the third layer may not provide the upper layer with an appropriate and direct support and so, may require the second layer or the middle layer.
A target of the research and industry on the reverse osmosis membrane field is improving or at least maintaining water flux without decreasing the degree of salt rejection for a long time to improve the efficiency of the membrane and the decrease of an operation cost. Instead of using uncertain novel chemicals, the importance on the surface modification on widely used polymers is strengthened. However, in this case, the most serious disadvantage is the fouling of the membrane inducing serious flux lowering during operation.
The main type of the fouling includes crystalline fouling such as a mineral scaling, a mineral deposition due to an excessive solution product, organic fouling such as the deposition of dissolved humic acid, oil, grease, etc., particle or colloidal fouling such as the deposition of clay, silt, a corrosive particle material, a debris and silica, and microbial fouling such as biofouling, attachment and accumulation of microorganism, and forming of a biofilm.
In order to decrease the fouling, various methods have been used. Generally, a plurality of coating layers is formed on the upper layer of the reverse osmosis membrane to modify the surface characteristic of the membrane through attaching a hydrophobic group or a hydrophilic group, and an electrically negative group or an electrically positive group, etc.
When an additional layer of the above-described diverse materials is formed to improve the reverse osmosis membrane, the thickness of the membrane may become large, and the maximization of target characteristics may become difficult due to the overlap of the coating layers including different materials.